Electrodeposition of copper and solutions therefor



United States Patent 3,287,236 ELECTRODEPOSITION OF COPPER AND SOLUTIONS THEREFOR Robert Brugger, Bernhausen, near Stuttgart, andGunter Voss, Heepen, Germany, assiguors to Langbem-Pfanhausen Werke A.G., Neuss (Rhine), Germany N0 Drawing. Filed 'Feb. 14, 1964, Ser. No. 344,838

6 Claims. (Cl. 20452) This invention relates to the electrodeposition of copper, and more particularly to the deposition of bright, smooth copper coatings free from pores from acid electrolytes.

It is known to produce such coatings from acid electrolytes by the use of organic or inorganic addition agents. When exacting requirements for brightness, leveling, absence of pores, and ductility of the deposit have to be met, it was necessary heretofore to employ at least two, and usually three or more different addition agents in the aqueous electrolyte consisting otherwise of an ionized copper salt and a suflicient amount of a strong acid to make the solution acid.

The addition agents conventionally employed usually include a surface tension reducing agent to prevent hydrogen bubbles from adhering to the plated surface and thus to avoid porosity of the coating. A second addition agent is used to control internal stresses in the electrodeposit. A third addition agent is the actual brightener. Frequently, a secondary brightener or leveling agent is necessary as a fourth addition agent to permit bright and smooth deposits to be formed directly on relatively rough base metal without polishing prior to plating.

The effective range of the addition agents is limited. Their concentration in the electrolyte decreases during plating operations due to chemical and electrolytic decomposition and because of drag-out losses. The concentration changes are not usually the same for each agent, and the agents must be replenished at different rates. Control of a copper plating solution'employing known auxiliary agents to produce bright, smooth, pore-free, and ductile coatings thus is difficult, and sometimes uncertain.

The object of the invention is the provision of an acid copper plating solution producing such coatings by means of a single addition agent.

Another object is the provision of a new class of brighteners for acid copper plating solutions which have good leveling elfects, prevent the formation of pores due to hydrogen bubbles, and do not embrittle the copper deposit formed.

Yet another object is the provision of brighteners which are insensitive to relatively high concentrations of impurities in the plating bath, and thus permit operation over extended periods without requiring purification of the electrolyte.

We have found that a wide variety of N-tetrahydropyranyl-Z substituted amides of car-boxylic and thiocarboxylic acids are effective leveling brighteners for acid copper plating solutions when employed in amounts as low as 0.2 millimole per liter, and that the coatings produced are pore-free and ductile when the concentration of the brightening agents of the invention is raised to their limit of solubility or 0.01 moles per liter whichever is lower.

The brighteners of the invention are of the formula 3,287,236 Patented Nov. 22, 1966 wherein X is either oxygon or sulfur, R is hydrogen or the radical of propane-w-sulfonic acid, and R may be any one of a large number of radicals to complete the structure of an N-tetrahydropyranyl-Z substituted carboxylic or thiocarboxylic acid amide, and more specifically that of an N-tetfahydropyranyl-Z- substituted urea or thiourea, as will hereinafter become apparent.

The brighteners of the invention in which R is hydrogen are prepared in yields of 20 to 70 percent from 2,3- dihydropyrane and amides corresponding to the brightening compounds to be produced in the presence of catalytic amounts of hydrogen chloride according to a method presented to the 139th meeting of the American Chemical Society, 1961, by A. I. Speziale, K. W. Ratts, and G. I. Marco (J. Org. Chem. 26, 4311-14, 1961; CA. 56, 14218, 1962; Angew. Chem. 1961 (73), 479). The compounds prepared in this manner readily react with propane sultone to form the corresponding N-n-propane-w-sulfonic acids.

According to the dual substituents R and X, the brightening agents of the invention are of four general types in each of which the nature of the substituent R is not particularly critical as long as it does not reduce the solubility of the compound below the lower limit of brightening eifectiveness.

The compounds of the first type in which X is oxygen and R is hydrogen are preferably employed as brighteners in concentrations between 0.5 millimole per liter and their upper limit of solubility or approximately five millimoles per liter, whichever is lower. No further improvement in brightness nor other desirable changes in deposit properties are achieved by exceeding the concentration of five millimoles per liter where solubility is adequate.

The following compounds are representative of the first type of brighteners of the invention:

The second type of brightening compounds of the invention differs from the first type by the substitution of a radical for the hydrogen atom in position R of the compounds of the first type. All compounds of the first type enumerated above for the sake of illustration may be converted to the second type by reaction with propane sultone. The twelve compounds so obtained are readily soluble, and their brightening effects increase over a wider range of concentrations than those of the first type of brighteners. The second type of brighteners is preferably employed at concentrations of 0.5 millimole per liter and higher, and their favorable effects increase up to a concentration of 0.01 mole per liter.

The third type of brighteners according to the invention differs from the first type by substitution of sulfur for the oxygen in position X. The thiamides of the third type are more effective than the corresponding substituted amides of the first type at equal concentrations, and are preferably employed over a range of 0.2 millimole to five millimoles per liter or to their limit of solubility whichever is lower. The following compounds are representative of the third type of brighteners:

( 13 N- tetrahydropyranyl-2 -thioacetamide 14) N-(tetrahydropyranyl-2)-thiopropionamide 15) N-(tetrahydropyranyl-2 -thiobutyramide 16) N-( tetrahydropyranyl-Z -thiobenzamide 17) N-(tetrahydropyranyl-2 -p-thiotoluamide 18) N-(tetrahydropyranyl-Z -thiourea 19) N- tetrahydropyranyl-Z -N'-acetylthiourea (20) N- (tetrahydropyranyl-2 -N'-carbethoxythiourea (21 N- (tetrahydropyranyl-2 -N-formylthiourea (22) N-(tetrahydropyranyl-2)-N-cyanothiourea (23) N- (tetrahydropyranyl-Z -N-carboxythiourea (24) N- (tetrahydropyranyl-2 -N'-phenylsulfonylthiourea 25) N- (tetrahydropyranyl-2 -N-nitrothiourea (26) N- (tetrahydropyranyl-2 -N-allylthiourea (27) N- tetrahydropyrany1-2 -N-phenylthiourea The fourth type of brightening agent of the invention differs from the second type by the, presence of sulfur in position X of the formula, and representative compounds of the fourth type are obtained by reaction of propane sultone wtih each of the compounds (13) to (27) enumerated hereinabove. The compounds of the fourth type are employed over the same range of concentrations as those of the second type.

The brightening agents of the invention are highly effective in both types of acid copper plating solutions presently in commercial use, namely the sulfate type and the fiuoborate type. Their use with electroplating solutions of these types is illustrated by the following examples, but it will be understood that the invention is not limited to the examples.

EXAMPLE 1 A copper plating solution was prepared from:

Copper sulfate, cryst., grams per liter 200 Sulfuric acid, C.P., grams per liter 50 N-(tetrahydropyranyl-2)-nicotinamide, moles per liter 0.0009

Copper was deposited from the solution under the following conditions:

Temperature, C. 22-26 Cathode current density, amps. per square foot (average) 45 Agitation (cathode movement), meters per minute 28 Fully bright deposits were formed on all surfaces on which the actual current density was between 4.5 and 72 amps. per square foot. Depressions in the base metal (brass) of 40 microns depth were practically completely obliterated when the average thickness of the deposit reached 20 microns.

These results are typical of the brightening compounds of the first type, and were substantially duplicated with each of the compounds enumerated above sub 1 to 12 in equimolecular amounts.

EXAMPLE 2 A copper plating electrolyte was prepared from Copper fluoborate, grams per liter 250 Fluoboric acid, grams per liter '30 N-(tetrahydropyranyl-Z) N acetylurea, moles per liter 0.0012

The following operating conditions were maintained during plating:

Temperature, C. 2.2-28

Cathode current density, amps. per square foot average 54 Agitation (cathode movement), meters per minute 28 The deposits formed were fully bright over an actual cathode current density range of 6.3 to 81 amps. per square foot as determined on a bent brass sheet electrode, and had a good leveling effect.

Closely similar effects were achieved with the other compounds of the first type enumerated above sub 1 to 12.

EXAMPLE 3 The composition and operating conditions of a copper plating solution were as follows:

Copper sulfate, cryst., grams per liter 200 Sulfuric acid, C.P., grams per liter 60 N (tetrahyd-ropyranyl-Z) N (n-propane-.w-sulfonic acid)-acetamide, moles per liter 0.003 Temperature, C. 20-28 Cathode current density, amps. per square foot Agitation (cathode movement), meters per minute 28 A copper plating solution of the composition listed below was used under the indicated opera-ting conditions:

Copper fluoborate, grams per liter 300 Fluoboric acid, grams per liter 40 'N (tetrahydropyranyl-Z) N (n-propane-w-sulfonic acid)-N'-ca-r-bethoxyurea, moles per liter 0.004

Temperature, C. 20-28 Cathode current density, amps. per square foot 63 Agitation (cathode movement), meters per minute 218 The copper coatings produced were fully bright over an actual cathode current density range of 5.4 to 90 amps. per square foot as determined with a bent brass sheet cathode, and had a very good leveling effect. Closely similar results were obtained with the other brightening compounds referred to in Example 3.

EXAMPLE 5 Mirror bright copper deposits tree from pores and of very good ductility were produced from an electrolyte 1 of the following composition under the operating conditions listed:

Copper sulfate, cryst., grams per liter 200 Sulfuric acid, C.P., grams per liter 60 N (tetrahydropyranyl-Z)-p-thiotoluamide, moles per liter 0.0006 Temperature, C. 22-26 Cathode current density, amps. per square foot average 45 Agitation (cathode movement), meters per minute 28 The copper plate was fully bright over an actual cathode current density range from 2.7 to 72 amps. per square 'foot. Scratches in the base metal having a depth of 40 microns were practically leveled when the average coating thickness reached 15 microns. Equimolecular amounts of the other compound-s of the third type listed above under numbers 13 to 27 gave corresponding results.

EXAMPLE 6 Mirror bright copper deposits were obtained from a fluo'borate electrolyte having the following composition, and operated under the listed conditions:

Copper fluoborate, grams per liter 250 Fluoboric acid, grams per liter 40 N (tetrahydropyranyl-Z) N carboxythiourea,

moles per liter 0.001 Temperature, C. 20-26 Cathode current density, amps. per square foot average 54 Agitation (cathode movement), meters per minute 2-8 The deposits were formed on objects of complex con- A sulfate type copper plating bath was prepared and operated as follows:

Copper sulfate, cryst., grams per liter 200 Sulfuric acid, C.P., grams per liter 60 N (tetrahydropyranyl 2) N (n propane wsulfonic -acid)-N-acetylthiourea, moles per liter 0.0015 Temperature, C. 20-28 Cathode current density, amps. per square foot 45 Agitation (cathode movement), meters per minute 2-8 The coatings produced were mirror bright from 1.8 to 72 amps. per square foot of actual cathode current density. They were ductile and free from visible pores. Irregularities in the base metal having a depth of 40 microns were completely leveled when the average thickness of the deposit reached microns.

Similarly favorable results were obtained with the other reaction products of propane sultone with the compounds of the third type listed sub 13 to 27. Peak performance was obtained from the several compounds at concentrations varying between 0.001 and 0.003 moles per liter.

EXAMPLE 8 Very ductile copper electrodeposits having .good develing action and being mirror bright were obtained from a fluoborate bath as follows:

Full brightness was achieved over an actual cathode current density range from 3.6 to 81 amps. per square foot.

The other compounds of the fourth type gave similar brilliantly bright copper deposits when employed as brighteners in the fluoborate electrolyte under the indicated operating conditions.

It will be appreciated that the acid copper sulfate and copper fluoborate electrolytes described in Examples 1 to 8 are entirely conventional in composition except for the brightening agents of the invention, and that the operating conditions employed are not unusual. The effects of the constituents in these solutions are well known, and those skilled in the art will find that variations in the concentrations of copper salts and free acids in these electrolytes afiect the bright deposits of the invention in a manner analogous to the effects produced in the absence of the brightening agents.

The temperature of the solutions is not critical. No effort was made in the plating runs reported on in the examples to hold the temperature within specific limits. The brightening agents of the invention are effective at temperatures as low as 10 C. or as high as 50f C. It is not usually necessary to employ copper sulfate or copper fluoborate plating solutions outside these extreme temperatures. An operating temperature between 10 C. and 50 C. is readily maintained without heating or cooling of the electrolyte under the ambient conditions of temperature prevailing in almost any plating plant.

The coatings produced do not lose their brightness or smoothness as their thickness increases. Coatings having a thickness of one millimeter (0.04 inch) are still fully bright, ductile, and dense.

The N-(tetrahydropyranyl-Z) amides of the invention are chemically stable in acid copper electrolytes when obviously unstable substituents in position R of the formula are avoided. They are consumed at a low rate during current passage through the electrolyte, and this rate is readily determined for a .given plating installation so that replenishment of brightening agents may be based on measurements of ampere hours of current passed.

Bright deposits can be obtained with the brightening agents of the invention up to cathode current densities of about amps. per square foot without agitation. Current densities much higher than 90 amps. per square foot are entirely practical with suitably rapid relative movement of electrolyte and plated object.

The brightening agents of the invention are relatively insensitive against contaminating ions such as those of lead, zinc, nickel, divalent and trivalent iron, and even hexavalent chromium. Copper plating solutions of the invention thus produce electrodeposits of the desired properties when made up of commercial chemicals of the grades normally employed in the electroplating industry Without requiring purification by chemical treatments, electrolysis at low current density, or the like.

While the invention has been described with particular reference to specific embodiments, it is to be understood that it is not limited thereto, but is to be construed broadly and restricted solely by the scope of the appended claims.

What is claimed is:

1. An aqueous acid copper plating electrolyte containing as a brightenin-g agent an N-(tetrahydropyranyl-Z) amide of a carboxylic acid dissolved in said electrolyte.

2. An aqueous acid copper plating electrolyte containing as a brightening agent an N-(tetrahydropyranyl-2) amide of a thiocarboxylic acid dissolved in said electrolyte.

3. An aqueous acid copper plating electrolyte containing as a brightening agent an N-(tetrahydropyranyl-2)- N-(propane-w-sulfonic acid) amide of a carboxylic acid dissolved in said electrolyte.

4. An aqueous acid copper plating electrolyte containing as a brightening agent an N-(tetrahydropyranyl-2)- N-propane-w-sulfonic acid amide of a thiocarboxylic acid dissolved in said electrolyte.

5. An aqueous acid copper plating electrolyte comprising a source of copper ions selected from the group consisting of copper sulfate and copper fluoborate, a source of hydrogen ions selected from the group consisting of sulfuric acid and fluoboric acid, and a brightening agent of the formula wherein X is a member of the group consisting of oxygen and sulfur, R is a member of the group consisting of hydrogen and the radical CH -CH SO H, and R is a member of the group consisting of lower alkyl, phenyl and pyridyl radicals, and radicals of the formula -NHR", wherein R" is a member of the group consisting of hydrogen, lower alkenyl, lower alkanoyl, carboxy, carbo- (lower)-alkoxy, phenylsulfonyl, nitro, formyl, cyano, and phenyl radicals, said sources and said brightening agent being dissolved in said electrolyte.

6. A method of producing a bright, smooth, pore-free, and ductile copper coating on a conductive object which comprises making said object a cathode in an electrolyte containing a source of copper ions selected from the group consisting of copper sulfate and copper fiuoborate, a source of hydrogen ions selected from the group consisting of sulfuric acid and hydrofluoric acid, and a brightening agent, said sources and said agent being dissolved in said solution, said agent being selected from the group consisting of N-(tetrahydropyranyl-Z) amides of carboxylic and thiocarboxylic acids, and N-(tetrahydropyranyl-2)- N-(propane-w-sulfonic acid) amides of carboxylic and thiocarboxylic acids, the concentration of said brightening agent in said electrolyte being between 0.2 and ten millimoles per liter, and the temperature of said electrolyte being between 10 C. and 50 C.

References Cited by the Examiner FOREIGN PATENTS 84,939 1/ 1958 Denmark.

JOHN H. MACK, Primary Examiner.

G. KAPLAN, Assistant Examiner. 

6. A METHOD OF PRODUCING A BRIGHT, SMOOTH, PORE-FREE, AND DUCTILE COPPER COATING ON A CONDUCTIVE OBJECT WHICH COMPRISES MAKING SAID OBJECT A CATHODE IN AN ELECTROLYTE CONTAINING A SOURCE OF COPPER IONS SELECTED FROM THE GROUP CONSISTING OF COPPER SULFATE AND COPPER FLUOBORATE, A SOURCE OF HYDROGEN IONS SELECTED FROM THE GROUP CONSISTING OF SULFURIC ACID AND HYDROFLUORIC ACID, AND A RIGHTENING AGENT, SAID SOURCES AND SAID AGENT BEING DISSOLVED IN SAID SOLUTION, SAID AGENT BEING SELECTED FROM THE GROUP CONSISTING OF N-(TETRAHYDROPYRANYL-2) A,IDES OF CARBOXYLIC AND THIOCARBOXYLIC ACIDS, AND N-(TETRAHYDROPYRANYL-2)N-(PROPANE-W-SULFONIC ACID) AMIDES OF CARBIOXYLIC AND THIOCARBOXYLIC ACIDS, THE CONCENTRATION OF SAID BRIGHTENING AGENT IN SAID ELECTROLYTE BEING BETWEEN 0.2 AND TEN MILLIMOLES PER LITER, AND THE TEMPRATURE OF SAID ELECTROLYTE BEING BETWEEN 10*C. AND 50*C. 